U.S. patent number 6,721,367 [Application Number 09/434,109] was granted by the patent office on 2004-04-13 for base station apparatus and radio communication method.
This patent grant is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Katsuhiko Hiramatsu, Kazuyuki Miya, Hideyuki Takahashi.
United States Patent |
6,721,367 |
Miya , et al. |
April 13, 2004 |
**Please see images for:
( Certificate of Correction ) ** |
Base station apparatus and radio communication method
Abstract
When switching to a path whose directivity changes greatly or a
path with a widely different propagation delay, transmission is
performed for both directivities for a certain period of time.
Then, transmission is performed for one directivity. When the
switching of transmission directivities is controlled, this allows
correct reception of signals and prevents instantaneous
interruption due to loss of synchronism even if transmission is
performed by switching to a path with a widely different
propagation delay.
Inventors: |
Miya; Kazuyuki (Kawasaki,
JP), Hiramatsu; Katsuhiko (Yokosuka, JP),
Takahashi; Hideyuki (Yokosuka, JP) |
Assignee: |
Matsushita Electric Industrial Co.,
Ltd. (Osaka, JP)
|
Family
ID: |
18109224 |
Appl.
No.: |
09/434,109 |
Filed: |
November 5, 1999 |
Foreign Application Priority Data
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Nov 10, 1998 [JP] |
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10-319354 |
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Current U.S.
Class: |
375/267; 375/299;
375/347; 455/101; 455/132 |
Current CPC
Class: |
H04B
7/0615 (20130101); H04W 52/42 (20130101) |
Current International
Class: |
H04B
7/005 (20060101); H04B 7/04 (20060101); H04B
7/06 (20060101); H04B 007/10 (); H04B 017/02 () |
Field of
Search: |
;375/267,130,347,260,259,299,341 ;455/137,132,101 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1170282 |
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Jan 1998 |
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CN |
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1195240 |
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Oct 1998 |
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CN |
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0639035 |
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Feb 1995 |
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EP |
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0851600 |
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Jul 1998 |
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EP |
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0869577 |
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Oct 1998 |
|
EP |
|
0639035 |
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Feb 1995 |
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GB |
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2313237 |
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Nov 1997 |
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GB |
|
6163118 |
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Apr 1986 |
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JP |
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10070494 |
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Mar 1998 |
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JP |
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98/27669 |
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Jun 1998 |
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WO |
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Other References
English Language Abstract of JP Appln. No. 10-070494. .
Partial English Language Translation of JP Appln. No.
61-3118..
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Primary Examiner: Bocure; Tesfaldet
Assistant Examiner: Ghulamali; Qutub
Attorney, Agent or Firm: Greenblum & Bernstein,
P.L.C.
Claims
What is claimed is:
1. A base station apparatus, comprising: a reception quality
detector that detects a first reception quality for a first path
and a second reception quality for a second path, in association
with signals received from a communication terminal apparatus via
the first path and the second path, the first path and the second
path having different arrival directions; a former that forms at
least one of a first directivity and a second directivity
respectively corresponding to the first path and the second path; a
transmitter that transmits signals by switching a transmission
directivity between the first directivity and the second
directivity in accordance with the first reception quality and the
second reception quality detected by the reception quality
detector, and the second reception quality is smaller than a
predetermined value, and subsequently changes the transmission
directivity to the second directivity.
2. The base station apparatus according to claim 1, further
comprising: a reception timing detector that detects a first
reception timing for the first path and a second reception timing
for the second path, wherein the transmitter transmits signals
using both the first directivity and the second directivity, when
the first reception timing is different from the second reception
timing.
3. The base station apparatus according to claim 1, wherein the
former comprises: an acquirer that acquires information from a
reception signal; and a selector that selects weighting factors
corresponding to at least one of the first directivity and the
second directivity based on the information, wherein the former
forms at least one of the first directivity and the second
directivity in accordance with the selected weighting factors.
4. The base station apparatus according to claim 3, wherein the
acquirer comprises a directional receptor that performs directional
reception at timings of a plurality of incoming signals, and
wherein the acquirer acquires the information from a signal
received from the directional receptor.
5. The base station apparatus according to claim 3, wherein the
former further comprises a receiver that receives a switching
control signal from a communicating party, and wherein the selector
selects the weighting factors based on the switching control
signal.
6. The base station apparatus according to claim 3, wherein the
selector selects the weighting factors based upon at least one of a
change in directivities of the first path and the second path, a
change in propagation loss and a change in propagation delay.
7. The base station apparatus according to claim 1, further
comprising a controller that controls transmission levels of
signals to be transmitted based on the first directivity and the
second directivity.
8. The base station apparatus according to claim 1, wherein the
first directivity is used in current communication and the second
directivity is based upon newly obtained weighting factors.
9. The base station apparatus according to claim 1, wherein the
transmitter performs time-multiplexing on signals to be transmitted
based on the first directivity and the second directivity in
different time slots.
10. A wireless communication method comprising: detecting a first
reception quality for a first path and a second reception quality
for a second path, in association with signals received from a
communication terminal apparatus via the first path and the second
path, the first path and the second path having different arrival
directions; forming at least one of a first directivity and a
second directivity respectively corresponding to the first path and
to the second path; transmitting signals by switching a
transmission directivity between the first directivity and the
second directivity in accordance with the first reception quality
and the second reception quality, wherein, while the transmission
directivity is being switched from the first directivity to the
second directivity, signals are temporarily transmitted using both
the first directivity and the second directivity, when a difference
between the first reception quality and the second reception
quality is smaller than a predetermined value, and subsequently the
transmission directivity is changed to the second directivity.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a base station apparatus and radio
communication method used in a digital radio communication
system.
2. Description of the Related Art
A propagation model in a radio communication is explained with
reference to FIG. 1. By way of example, suppose the number of
antennas of the radio communication apparatus (base station
apparatus) is 3. In FIG. 1, two paths A and B indicate downlink
(transmission from a base station to terminal) propagation paths. A
signal transmitted from base station apparatus 1 is reflected by
building 2 and arrives at an antenna of terminal apparatus 3. Such
a propagation path is called a "multi-path propagation path" and
communication quality generally deteriorates if this multi-path
propagation cannot be compensated. In this example, suppose the
signal from building 2 is received by the receiving side with a
delay within the range of its time resolution. Transmission
directivity in this case is shown in FIG. 2.
Thus, if this signal contains a great delay, this delay may be a
major factor of deterioration of the communication quality. To
suppress multi-path propagation, it is desirable to transmit
signals to either path A or path B. Furthermore, a communication
system such as a CDMA transmission system in which a same band and
time are shared can suppress interference with other stations by
narrowing the range of transmission directivity, providing an
effective way of achieving high frequency utilization efficiency.
Therefore, it is extremely important to detect a direction of an
optimal communication quality and perform transmissions focusing on
that direction.
FIG. 3A to FIG. 3C are delay profiles showing the propagation path
characteristics of path A and path B in FIG. 1. In FIG. 3, the
horizontal axis represents the time and the vertical
axis-represents the propagation loss. That is, t0 and t1 on the
receiving side represent timings of path A and path B, respectively
and the height difference represents a difference in the reception
level (difference in propagation loss). The fact that the reception
timing differs between path A and path B means that path A and path
B differ in the propagation distance.
A delay profile generally changes as a terminal moves. That is, the
communication quality of each of path A and path B changes. FIG. 3A
shows that the communication quality of path A is better, while
FIG. 3B shows that both paths have equivalent levels of
communication quality and FIG. 3C shows that the communication
quality of path B is better.
A conventional base station apparatus is explained below. FIG. 4 is
a block diagram showing a configuration of a base station apparatus
that carries out conventional adaptive array transmission. By way
of example, suppose the number of antennas is 3.
The transmitting side of this terminal modulates a transmission
signal by modulation circuit 11. A plurality of reception weighting
factors calculated by weighting factor calculation circuit 12 based
on an advance information signal are output to selection circuit 13
where an optimal weighting factor is selected, and processing
circuit 14 performs a multiplication (generally complex
multiplication) using this weighting factor. Naturally, it is also
possible to perform a multiplication after calculating only an
optimal weighting factor. Then, radio transmission circuit 15
carries out frequency conversion and amplification on the
transmission signal and transmits it from antennas.
In a propagation environment as shown in the delay profiles in FIG.
3, the base station apparatus above performs transmission by
forming directivity in the direction of path A when the
communication quality of path A is better as shown in FIG. 3A. The
base station apparatus also performs transmission by forming
directivity in the direction of path B when the communication
quality of path B is better as shown in FIG. 3C. On the other hand,
if path A and path B have equivalent levels of communication
quality as shown in FIG. 3B, the base station apparatus performs
transmission by forming directivity in either direction.
Therefore, if the other end of communication is a moving terminal,
the delay profiles change with time, and therefore, the base
station apparatus shown in FIG. 4 can always perform transmission
with array antennas of an optimal communication quality by making
its weighting factor selection circuit switch a weighting factor
according to a change in the delay profiles.
Here, transmission timing is generally not changed in accordance
with directivity switching. This is because in the case of
continuous transmission, changing transmission timing will cause
problems such as discontinuation or overlap of a transmission
signal and collapse of orthogonality (code orthogonality in the
case of CDMA, and time orthogonality in the case of TDMA) with
other channels with which the transmission signal is multiplexed.
etc.
The calculation of the receiving side at the other end of
communication (terminal) is explained using FIG. 5. On the terminal
side, a reception signal received by an antenna is output to radio
reception circuit 22 via antenna duplexer 21. Radio reception
circuit 22 carries out amplification, frequency conversion and A/D
conversion on the reception signal and extracts a baseband signal
or IF signal.
In a CDMA system using a spread spectrum (SS) communication system,
a reception signal is output to correlator (or matched filter) 23
and despread by the same spreading code as that used for spreading
processing on the transmitting side. The despread signal is output
to timing detection circuit 24. Timing detection circuit 24
calculates the power of the correlator output and detects time to
when the power is large. This timing to is output to sampling
circuit 25. Sampling circuit sends the reception signal with timing
t0 to demodulation circuit 26. Demodulation circuit 26 demodulates
and outputs the reception signal.
On the other hand, a non-CDMA communication system generally sends
the extracted baseband signal or IF signal to timing detection
circuit 24. Timing detection circuit 24 calculates an optimal
reception timing. The optimal reception timing is calculated, for
example, by the transmitter side embedding a pattern known to both
the transmitter and receiver in a frame and transmitting this
signal. The receiver side performs A/D conversion with several to
over ten times the one-symbol time and performs a correlation
calculation with the known symbol. Then, the receiver side detects
timing to when the power resulting from the correlation calculation
is large. This timing to is output to sampling circuit 25. Sampling
circuit 25 sends the reception signal of timing t0 to demodulation
circuit 26. Demodulation circuit 26 demodulates and outputs the
reception signal.
On the other hand, the transmission signal is modulated by
modulation circuit 27, that is, in the CDMA transmission system,
the transmission signal is spread using a predetermined spreading
code. The modulated signal is frequency-converted and amplified by
radio transmission circuit 28 and transmitted from an antenna via
duplexer 21.
Then, the following is an explanation of the calculation of a base
station in a radio communication system when adaptive array
reception and adaptive array transmission based on information
thereof are applied. The calculations of the conventional base
station in FIG. 6 and the terminal in FIG. 5 are explained. By way
of example, suppose the number of antennas of the apparatus is
3.
First, the uplink is explained. The terminal on its transmitting
side modulates a transmission signal by modulation circuit 27. This
modulated signal is frequency-converted and amplified by radio
transmission circuit 28 and transmitted from the antennas via
antenna duplexer 21.
The base station sends signals received from its antennas to radio
reception circuit 32 via respective antenna duplexers 31. Radio
reception circuit 32 carries out amplification, frequency
conversion and A/D conversion on the reception signals and extracts
baseband signals or IF signals. If the transmission and reception
signals have the same frequency (TDD transmission), changeover
switches are used instead of duplexers. These signals are output to
timing detection circuit 34.
Timing detection circuit 34 calculates an optimal reception timing.
The optimal reception timing is calculated, for example, by
embedding a pattern known to both a transmitter and receiver in a
frame and transmitting this signal from the transmitter. The
receiver performs A/D conversion with several to over ten times the
one-symbol time and performs a correlation calculation with the
known symbol. Then, the receiver detects timing t0 when the power
resulting from the correlation calculation is large. This timing t0
is output to sampling circuit 35.
Sampling circuit 35 sends the reception signal with timing t0 to
adaptive array antenna reception circuit 36. Adaptive array antenna
reception circuit 36 combines the reception signals from the three
antennas so that a desired wave or SIR reaches a maximum value for
each timing. Then, adaptive array antenna reception circuit 36
outputs the reception signals and reception weighting factors to be
multiplied on the reception signals of the respective antennas.
These weighting factors form reception directivity.
If adaptive array antenna processing is performed so as to extract
a desired signal, the directivity is directed to the desired
signal, generating a part with small directivity (called "null") in
an unnecessary signal (signal identical to the desired signal,
which arrives at a different time because the propagation path is
different, or signal from another transmitter). The number of null
points is known to be (the number of array antennas -1) and if the
number of antennas is 3, 2 null points are formed.
In the case of a CDMA system using a spread spectrum (SS)
communication system, correlator (or matched filter) 33 performs
despreading using the same spreading code as that used for
spreading processing for baseband signals or IF signals on the
transmitter side. The despread signals are output to timing
detection circuit 34. Timing detection circuit 34 calculates the
power of the correlator output and detects times t0 and t1 when the
power is large. These timings t0 and t1 are output to sampling
circuit 35.
Sampling circuit 35 sends the reception signals with timings t0 and
t1 to adaptive array antenna reception circuit 36. Adaptive array
antenna reception circuit 36 combines the reception signals from
the three antennas so that a desired wave or SIR reaches a maximum
value for each of reception timings t0 and t1 using the weighting
factors calculated by reception weighting factor calculation
circuit 37 and finally combines additional reception signals
corresponding to 2 paths. Then, adaptive array antenna reception
circuit 36 outputs the resultant reception signals and two
reception weighting factor sets to be multiplied on the reception
signals of the respective antennas. These two weighting factor sets
form reception directivities with reception timings t0 and t1,
respectively.
Then, the downlink is explained. The base station modulates a
transmission signal by modulation circuit 38. Transmission
weighting factor calculation circuit 39 regenerates transmission
weighting factors based on the reception weighting factors. Then,
processing circuit 40 performs a multiplication (generally complex
multiplication) by an optimal transmission weighting factor after
selecting a weighting factor set by selection circuit 41. At this
time, as explained in the calculation of the base station shown in
FIG. 4, weighting factor selection circuit 41 can always perform
transmission with array antennas of an optimal communication
quality by switching between the two transmission weighting factor
sets according to changes in the delay profiles.
As shown above, transmitting signals with the same directivity
pattern as the reception directivity pattern based on the weighting
factors of the reception signals combined through an adaptive array
antenna prevents signals being transmitted in directions of
unnecessary signals that have arrived, and therefore allows the
transmitting side to compensate the multi-path propagation path.
This eliminates the need for providing the receiver (terminal side)
with high-class devices such as equalizer.
Avoiding transmitting signals in directions of unnecessary signals
that have arrived limits the reach of radio waves transmitted,
improving thus the downlink frequency utilization efficiency. Since
transmission is also performed via a propagation path with the
desired wave power on the uplink or with great SIR taking advantage
of reversibility of the propagation path, the desired wave power or
SIR increases on the downlink as well.
However, when the switching of transmission directivities is
controlled according to the conventional system described above, if
transmission is performed by selecting a path with a widely
different propagation delay, the reception timing on the receiving
side suddenly changes, which causes problems such as preventing it
from receiving signals correctly until the receiving side detects a
new reception timing and switches directivities or causing
instantaneous interruption of a reception signal due to loss of
synchronism.
In a CDMA system using spread spectrum communications in
particular, when the switching of transmission directivities is
controlled using reception directivities through a reception
adaptive array, if directivity transmission is performed by
selecting a path with a widely different propagation delay, the
propagation path suddenly changes, which causes problems such as
preventing the terminal from receiving signals correctly because a
search and finger assignment cannot follow the change or causing
instantaneous interruption of a reception signal due to loss of
synchronism.
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide a base
station apparatus and radio communication method capable of
receiving a signal correctly and preventing instantaneous
interruption due to loss of synchronism when the switching of
transmission directivities is controlled and even when transmission
is performed by selecting a path with a widely different
propagation delay.
The present inventor has come up with the present invention by
discovering that it is possible to solve the problems of the
propagation path suddenly changing preventing the terminal from
receiving signals correctly because a search and finger assignment
cannot follow the change or loss of synchronism even if adaptive
array transmission is performed by selecting a path with a greatly
different propagation delay.
That is, when selecting a path where a directivity changes greatly,
the present invention performs transmission in both directivities
like soft handover and the terminal performs reception by combining
them. Then, the terminal switches to one directivity according to
the reception level. In this specification, this technology is
called "path handover (PHO)."
This PHO is especially effective for directivity switching when
introducing an adaptive array antenna for the downlink of a W-CDMA
system. PHO makes it possible to improve the reception
characteristic on the terminal and prevent instantaneous
interruption of a reception.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects and features of the invention will
appear more fully hereinafter from a consideration of the following
description taken in connection with the accompanying drawing
wherein one example is illustrated by way of example, in which;
FIG. 1 is a diagram showing a propagation model in a radio
communication system;
FIG. 2 is a conceptual diagram showing transmission directivity in
a radio communication;
FIGS. 3A to 3C are diagrams showing a delay profile of a reception
signal;
FIG. 4 is a block diagram showing a conventional base station;
FIG. 5 is a block diagram showing a configuration of a
terminal;
FIG. 6 is a block diagram showing another configuration of the
conventional base station;
FIG. 7 is a block diagram showing a configuration of a base station
according to Embodiment 1 of the present invention;
FIG. 8 is a block diagram showing a configuration of a terminal
according to the embodiment above;
FIG. 9 is a diagram showing a configuration of a combination
circuit of the base station according to the embodiment above;
FIG. 10 is a diagram showing another configuration of the
combination circuit of the base station according to the embodiment
above;
FIG. 11 is a block diagram showing a configuration of a base
station according to Embodiment 2 of the present invention;
FIG. 12 and FIG. 13 are block diagrams showing another
configuration of the base station according to the embodiment
above;
FIGS. 14A to 14C are diagrams to explain threshold switching
control of PHO according to the embodiment above;
FIG. 15 is a diagram to explain time slots in a TDMA transmission
system; and
FIG. 16 is a diagram showing a configuration of a combination
circuit in a base station according to Embodiment 3 of the present
invention.
DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENTS When switching to a path where a directivity
changes greatly, the base station apparatus and radio communication
method of the present invention perform transmission in both
directivities such as soft handover and the terminal performs
reception by combining them. Then, one directivity is switched
according to the reception level. The base station determines this
switching to PHO. Switching to one path (directivity) is performed
by two methods; method of the base station autonomously determining
the switching or feedback method by notifying a shift to PHO to a
mobile station beforehand. The method of the base station
autonomously determining the switching is further divided into a
method of the mobile station determining the switching at the path
reception level of uplink adaptive array antenna reception and
method of the mobile station determining the switching at the
reception level of each PHO path.
Furthermore, the base station selects a reception path, which is
the source of a transmission directivity, determines whether the
directivity of each path is widely different and performs adaptive
array antenna transmission with both directivities. In this case,
the transmission level of each directivity is controlled.
The present invention is also applicable to a TDMA transmission
system. In this case, just two receivers are enough for the mobile
station. In a TDMA/CDMA system, the present invention can also be
implemented with a single receiver if processing that allows
time-sharing of two paths is provided.
With reference now to the attached drawings, the embodiments of the
present invention are explained in detail below.
Embodiment 1
FIG. 7 is a block diagram showing a configuration of a base station
according to Embodiment 1 of the present invention. FIG. 8 is a
block diagram showing a configuration of a terminal according to
Embodiment 1 of the present invention. FIG. 7 describes only the
transmitting side. Here, a CDMA system using a spread spectrum (SS)
communication system is assumed.
First, the calculation of the base station shown in FIG. 7 is
explained. By way of example, suppose the number of antennas is 3.
A transmission signal is modulated by modulation circuit 101. On
the other hand, of a plurality of transmission weighting factors
calculated by weighting factor calculation circuit 102 based on an
advance information signal such as PHO shift, the most suitable one
or two weighting factors are selected by weighting factor selection
circuit 103 and multiplied by processing circuits 104 and 105.
These transmission signals are then combined (multiplexed) by
combination circuit 106, frequency-converted and amplified by radio
transmission circuit 107 and transmitted from antennas.
The calculation of selection circuit 103 and the calculation of
combination circuit 106 are explained in correspondence with the
delay profiles shown in FIG. 3. When the delay profile changes from
FIG. 3A to FIG. 3B then to FIG. 3C, the communication quality of
path A is obviously better than path B in FIG. 3A, and transmission
is performed by forming directivity only in the direction of path
A. At this time, selection circuit 103 only selects the weighting
factor of path A to carry out a product sum calculation.
Furthermore, combination circuit 106 does not combine signals and
sends only the multiplication signal of one path to radio
transmission circuit 107.
On the other hand, if the delay profile changes to FIG. 3B, path A
and path B have equivalent levels of communication quality.
Conventionally, transmission would be performed by forming a
directivity only in either direction, but in the present invention,
directivities in the respective directions of path A and path B are
formed and signals to be transmitted according to respective
directivities are combined and transmitted.
That is, selection circuit 103 selects two weighting factors of
path A and path B and performs product sum calculations on their
respective modulated signals. Then, combination circuit 106
combines the two signals for each antenna and sends the combined
signal to radio transmission circuit 107.
When the delay profile changes to FIG. 3C, the communication
quality of path B is better as opposed to FIG. 3A, and transmission
is performed by forming a directivity only in the direction of path
B. At this time, selection circuit 103 only selects the weighting
factor of path B and performs a product sum calculation. Then,
combination circuit 106 does not combine signals and sends only the
multiplication signal of one path to radio transmission circuit
107.
Here, the combination circuit is explained using FIG. 9 and FIG.
10. FIG. 9 shows a basic combination circuit and FIG. 10 shows a
combination circuit with a control circuit that individually
controls the transmission levels of signals with respective
directivities added. That is, in FIG. 9, each signal subjected to a
product sum calculation by a weighting factor is multiplied by a
coefficient according to the respective transmission levels and
combined in combination circuit 301. In this case, transmission of
only one signal in the above calculation is performed by setting
the transmission level of another signal to 0.
The combination circuit shown in FIG. 10 incorporates transmission
level control circuit 403 that individually controls the
transmission levels of respective signals subjected to a product
sum calculation, and the signals subjected to a product sum
calculation are multiplied by coefficients by multiplication
sections 401 and 402. The signals whose transmission levels have
been individually controlled are combined by combination section
404.
Then, the calculation of the receiving side of the terminal at the
other end communication is explained using FIG. 8. On the terminal
side, a signal received by an antenna is output to radio reception
circuit 202 via antenna duplexer 201. Radio reception circuit 202
performs amplification, frequency conversion and A/D conversion on
the reception signal and extracts a baseband signal or IF signal.
This baseband signal or IF signal is despread using the same
spreading code as that used on the transmitting side by correlator
(or matched filter) 203.
Then, the despread signal is output to timing detection circuit
204. Timing detection circuit 204 calculates the power of the
correlator output and detects time t1 when the power is large. This
timing t1 is output to sampling circuit 205. Sampling circuit 205
sends the reception signal with timing t1 to demodulation circuit
206. Demodulation circuit 206 demodulates and outputs the reception
signal. In the CDMA system, timing detection circuit 204 performs a
search and finger assignment.
On the other hand, a transmission signal is modulated by modulation
circuit 207, and in the CDMA transmission system the signal is
spread using a prescribed spreading code. The modulated signal is
frequency-converted and amplified by radio transmission circuit 208
and transmitted from the antenna via duplexer 201.
As shown above, the weighting factor selection circuit does not
simply switch a weighting factor from path A to path B according to
a change in the delay profile, but selects weighting factors of
path A and path B when both have equivalent levels of power and
transmission is performed with directivities set for both paths.
This makes it possible not only to always transmit signals with
array antennas with an optimal communication quality, but also to
detect a new timing (a search and finger assignment in CDMA) while
transmitting with both directivities when the switching of
transmission directivities is controlled, which prevents the timing
detection circuit in the terminal from failing to perform a
switching calculation in time even if directivity transmission is
performed by switching to a path with a widely different
propagation delay and also prevents instantaneous interruption of a
reception signal.
Embodiment 2
FIG. 11 is a block diagram showing a configuration of a base
station according to Embodiment 2 of the present invention. The
present embodiment assumes a CDMA system using a spread spectrum
(SS) communication system. Embodiment 2 is explained using a base
station to which adaptive array transmission based on adaptive
array reception and its information is applied and the terminal at
the other end of communication shown in FIG. 8. By way of example,
suppose the number of antennas in the base station is 3.
First, the uplink is explained. The terminal on its transmitting
side modulates a transmission signal by modulation circuit 207.
This modulated signal is frequency-converted and amplified by radio
transmission circuit 208 and transmitted from the antenna via
antenna duplexer 201.
The base station sends signals received from the antennas to radio
reception circuit 502 via antenna duplexers 501. Radio reception
circuit 502 carries out amplification, frequency conversion and A/D
conversion on the reception signals and extracts baseband signals
or IF signals. If the transmission and reception signals have the
same frequency (TDD transmission), changeover switches are used
instead of duplexers.
These baseband signals or IF signals are output to correlator (or
matched filter) 503. Correlator 503 despreads these signals using
the same spreading code as that used on the transmitter side. Then,
the despread signals are output to timing detection circuit 504.
Timing detection circuit 504 calculates the power of the correlator
output and detects times to and t1 when the power is large and
sends these timings to and t1 to sampling circuit 505.
Sampling circuit 505 sends the reception signals with timings to
and t1 to adaptive array antenna reception circuit 506. Adaptive
array antenna reception circuit 506 combines the reception signals
from the three antennas so that a desired wave or SIR reaches a
maximum value for each of reception timings to and t1 using the
weighting factors and finally combines additional reception signals
corresponding to 2 paths. Then, adaptive array antenna reception
circuit 506 outputs the resultant reception signals and two
reception weighting factor sets to be multiplied on the reception
signal of each antenna.
Based on these two weighting factor sets, reception directivities
with reception timings t0 and t1 are formed, respectively. That is,
the two weighting factor sets from adaptive array antenna reception
circuit 506 are output to reception weighting factor calculation
circuit 507 where reception weighting factors are calculated.
Reception directivities are formed by calculating these reception
weighting factors. In this example, two reception timings t0 and t1
are detected, but it is obvious that 3 or more reception timings
can also be detected.
Then, the downlink is explained. The base station modulates a
transmission signal by modulation circuit 508. On the other hand,
transmission weighting factor calculation circuit 509 regenerates
transmission weighting factors based on the reception weighting
factors calculated by reception weighting factor calculation
circuit 507. This transmission weighting factor is output to
weighting factor selection circuit 510. Weighting factor selection
circuit 510 selects an optimal weighting factor from among a
plurality of transmission weighting factors and sends them to
processing circuits 511 and 512 and performs multiplication
processing on the signal modulated by modulation circuit 508.
Weighting factor selection circuit 510 selects a weighting factor
based on the reception quality from reception quality detection
circuit 513. This reception quality is detected by adaptive array
antenna reception circuit 506 for the reception signal.
Transmission weighting factor calculation circuit 509, weighting
factor selection circuit 510 and reception quality detection
circuit 513 form a PHO processing section. Here, the PHO processing
section has the configuration above because a reception quality is
used as weighting factor selection information, but the
configuration of the PHO processing section may be different if
other information (reception timing and directivity pattern) is
used as the weighting factor selection information.
Then, the signals subjected to product sum calculation processing
are output to combination circuit 514 where the signals are
combined (multiplexed) and output to radio transmission circuit
515. Radio transmission circuit 515 performs frequency conversion
and amplification on the signals and transmits these signals from
the antennas via duplexers 501.
Here, weighting factor selection circuit 510 of the PHO processing
section is explained.
Weighting factor selection circuit 510 selects weighting factors
based on various kinds of information. The first information is
reception quality with each reception directivity or a difference
in reception quality between reception directivities. This
reception quality includes, for example, the level of a desired
wave or SIR. Weighting factor selection circuit 510 selects a path
for directivity transmission based on this reception quality
information and the number of paths.
Then, the second information is each reception timing or a
difference between reception timings. A path with a wide difference
between reception timings is likely to have different spatial
directivities. Taking account of this tendency, it is determined
whether a shift should be made to a PHO state (directivity
transmission with 2 paths or more) only based on the timing
difference without directly comparing reception directivities. This
control can be implemented with the base station shown in FIG. 12.
In FIG. 12, a reception timing detected by timing detection circuit
504 is output to weighting factor selection circuit 510 of the PHO
processing section. Then, an optimal weighting factor is selected
based on the reception timings or their difference. The parts in
FIG. 12 identical to those in FIG. 11 are assigned the same numbers
and their explanations are omitted.
Then, the third information is a directivity pattern of each
reception directivity. In this case, PHO is determined after
comparing directivities of paths to be selected (reception
directivities or transmission directivities) and determining
whether directivities are changed when paths are switched, that is,
whether the propagation delay changes greatly. Therefore, if
directivities change when paths are switched, PHO is performed.
More specifically, this control is performed by storing the
weighting factors calculated by reception weighting factor
calculation circuit 507 or transmission weighting factor
calculation circuit 509, comparing these weighting factors and
newly calculated weighting factors and determining the presence of
a change in directivities.
The method of using this directivity pattern information can be
combined with the method of using the above reception timing
information.
When using the first to third information above, it is desirable to
control the information using a threshold. When using a reception
quality in particular, control using a threshold is essential. For
example, if the reception quality of a certain path is within
.alpha. [dB] from the reception quality of a maximum path, the
system controls so that transmission be performed in the direction
of the path and if .alpha. [dB] is exceeded, the system controls so
that the transmission in that direction be stopped. Such control
allows high-precision control.
PHO using the weighting factor selection above is autonomously
determined and performed by the base station. On the other hand,
PHO can also be performed by the base station by getting feedback
through a switching control signal from the terminal. That is, the
terminal sends information such as the number of paths selected,
paths to be selected through the uplink to the base station as a
control signal and the base station determines PHO based on that
signal or in combination with other information as well.
This control can be implemented with the base station shown in FIG.
13. That is, in FIG. 13, a switching control signal is output from
the terminal to weighting factor selection circuit 510, where
weighting factors are selected based on the switching control
signal. The parts in FIG. 13 identical to those in FIG. 11 are
assigned the same numbers and their explanations are omitted.
It is desirable to select the weighting factors above as
appropriate by a change in directivities of at least two paths,
change in propagation loss or change in propagation delay. It is
further desirable that the directivities of at least two paths
include the directivities being currently in communication and
newly obtained directivities. These allow more accurate
control.
As the input information for combination circuit 514, the number of
paths selected and reception quality information, etc. are input
mainly as control of the transmission level. The number of paths
selected is used to determine how many paths are combined and
transmitted. The reception quality information is used to control
the transmission level of each path.
Then, the calculation of weighting factor selection circuit 510 and
the calculation of combination circuit 514 are explained using the
delay profiles in FIG. 14. Here, .alpha. [dB] is set as a switching
threshold.
If the delay profile in timing detection circuit 504 on the
receiving side changes from FIG. 14A to FIG. 14B then to FIG. 14C,
the receiving side detects times t0 and t1 when the reception power
is large, sends the reception signals with these timings t0 and t1
to adaptive array reception circuit 506 and combines and receives
the directional reception signals.
On the other hand, on the transmitting side, weighting factor
selection circuit 510 selects a weighting factor based on the
reception quality information of each path from reception quality
detection circuit 513. In FIG. 14A, the reception quality of path A
excels that of path B sufficiently, and therefore only path A is
selected and transmission is performed by forming directivity only
in the direction of path A using the transmission weighting factor.
At this time, weighting factor selection circuit 510 only selects
the weighting factor of path A and performs a product sum
calculation using this weighting factor. Combination circuit 514
does not combine signals. Thus, only a signal multiplied by the
weighting factor of path A is output to radio transmission circuit
515, subjected to radio transmission processing and then
transmitted.
On the other hand, if the delay profile changes as shown in FIG.
14B, the reception quality of path A and path B is within threshold
.alpha. dB. At this time, the present invention forms directivities
in directions of path A and path B and combines and transmits them.
That is, weighting factor selection circuit 510 selects two
weighting factors of path A and path B and performs product sum
calculations on the demodulated signals using these weighting
factors. Then, combination circuit 514 combines two signals for
each antenna and sends it to radio transmission circuit 515 to
subject the signal to radio transmission processing and send
it.
If the delay profile changes as shown in FIG. 14C, the
communication quality of path B is better as opposed to FIG. 14A,
and therefore a directivity is formed only in the direction of path
B and transmitted. That is, the weighting factor selection circuit
only selects the weighting factor of path B and performs a product
sum calculation using this weighting factor. Furthermore,
combination circuit 514 does not combine signals. Thus, only a
signal multiplied by the weighting factor of path A is output to
radio transmission circuit 515 to subject the signal to radio
transmission processing and send it.
The configuration of combination circuit 514 is the same as that
explained in Embodiment 1, and its explanation is omitted.
As shown above, the weighting factor selection circuit does not
simply switch a weighting factor from path A to path B in
accordance with a change of the delay profile but selects two
weighting factors of path A and path B when both have equivalent
levels of power and performs transmission with directivities for
both. This not only allows transmission with array antennas with an
optimal communication quality all the time but also detection of a
new timing (a search and finger assignment in the case of CDMA)
while transmitting with both directivities when the switching of
transmission directivities is controlled, which prevents the timing
detection circuit in the terminal from failing to perform switching
calculation in time (failing to perform a search and finger
assignment in time) even if directivity transmission is performed
by switching to a path with a widely different propagation delay,
and prevents instantaneous interruption of a reception signal.
Embodiment 3
The present embodiment describes a case where PHO is applied to a
TDMA transmission system. A radio communication apparatus in this
case has basically the same configuration as that of the base
station shown in FIG. 7. It is different from the base station
shown in FIG. 7 in that it has a different combination circuit.
A TDMA transmission system performs transmission in a time slot
configuration as shown in FIG. 15. In the TDMA transmission system,
it is desirable to suppress multi-path propagation by transmitting
signals to either path A or path B. In this case, each signal is
transmitted using a separate slot.
The combination circuit in this case contains transmission level
control circuit 1003 as shown in FIG. 16 that individually controls
the transmission level of each signal subjected to a product sum
calculation. In this configuration, a signal subjected to a product
sum calculation is multiplied by coefficients by multiplication
sections 1001 and 1002, respectively. Then, signals whose
transmission level is individually controlled are switched at a
timing corresponding to its time slot by switching section 1004. In
the TDMA system, transmission slot position information, that is,
position information of slots to be time-multiplexed when two or
more paths are transmitted is input to combination circuit 514.
For example, if the power of path A and path B have equivalent
levels of power, the two weighting factors of path A and path B are
selected and transmission with directivities for both paths is
performed. In this case, path A is output with time slot 1 (TS1)
and path B is output with time slot 2 (TS2).
This not only allows transmission with array antennas with an
optimal communication quality all the time but also detection of a
new timing while transmitting with both directivities when the
switching of transmission directivities is controlled, which
prevents the timing detection circuit in the terminal from failing
to perform switching calculation in time even if directivity
transmission is performed by switching to a path with a widely
different propagation delay, and prevents instantaneous
interruption of a reception signal.
The base station apparatus and radio communication method of the
present invention is applicable to a base station apparatus and
communication terminal apparatus such as a mobile station in a
radio communication system.
The present invention is not limited to the embodiments above, but
can be implemented with various modifications. Therefore, it can be
implemented by combining the technologies in the embodiments above
as appropriate.
As described above, since the base station apparatus and radio
communication method in the present invention use path handover
when the switching of directivities is controlled, the present
invention prevents the timing detection circuit in the terminal
from failing to perform switching calculation in time even if
directivity transmission is performed by switching to a path with a
widely different propagation delay and prevents instantaneous
interruption of a reception signal.
The present invention is valid for directivity switching in
adaptive array antenna transmission in particular. The present
invention is not limited to the above described embodiments, and
various variations and modifications may be possible without
departing from the scope of the present invention.
This application is based on the Japanese Patent Application No.
HEI 10-319354 filed on Nov. 10, 1998, entire content of which is
expressly incorporated by reference herein.
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